Pliocene to Quaternary Terrigenous and Calcareous Succession at ODP Site 1119 Off New Zealand as a Drift Reservoir Analogue

Nolasco, Jasmyn M. and Marsaglia, Kathleen M.
[email protected]

ODP (Ocean Drilling Program) drill Site 1119 penetrated a drift succession on the Canterbury slope, ~100 km off the eastern coast of South Island, New Zealand. Prompted by northward flowing currents, drift accumulation began on the margin in the Late Oligocene (~25 Ma) and has continued through the Quaternary. Terrigenous sand input is thought to have been controlled by uplift associated with the Alpine Fault plate boundary to the west and eustasy that created cyclicity in sandy input at ODP Site 1119 during the last ~4 million years.

Thirty-five sandy samples from the Pliocene to the Pleistocene section were collected for the study and were sieved into very fine, fine, and medium sand fractions. These were then made into thin-sections and petrographically analyzed. Up to 400 grains were counted on each slide using the Gazzi-Dickinson method to determine detrital and biogenic modes. Data were recalculated and plotted on ternary diagrams for analysis.

The terrigenous sand is quartzo-feldspathic, with mean QFL values of 36%Q, 53%F, and 11%L. High plagioclase feldspar, metamorphic rock fragment, and chlorite content indicate an Otago Schist provenance via the Clutha River, ~150 km to the south. There are some differences in foram types with grain size. Benthic forams are more abundant in the very fine sand fraction and planktic forams are concentrated in the fine sand fraction, possibly related to density differences between them. Mollusc fragments dominate the medium sand fraction.

This work provides a better understanding of the textural and compositional variability of sandy drift successions that have been discussed as potential hydrocarbon reservoirs in other ocean basins.

AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013